1. Field of the Invention
The present invention relates to a method and an apparatus for preventing wrong use of a magnetic recording medium such as an advance payment card, for example, which is generally called a prepaid card.
2. Description of the Related Art
A card (magnetic card) in which information is recorded by the magnetic recording system has been used in various fields. For example, in a prepaid card (advance payment card) used for a public telephone set and an automatic ticket selling machine, various pieces of information such as available metering rates and amount of money information equivalent to the payment are recorded. Upon purchasing of this prepaid card, a telephone call can be made and a ticket can also be purchased using the prepaid card without use of small money.
In this case, the available metering rate and amount of money information recorded in the prepaid card are updated to the latest information each time when the prepaid card is used.
Such update process is performed using, for example, a prepaid card (magnetic card) update apparatus as shown in FIG. 1. This update apparatus is mounted within the apparatus which can use a prepaid card, for example, such as a public telephone set an automatic ticket selling machine, etc.
As shown in FIG. 1, signal (information) recorded in the magnetic card 50 is read by a reading means 1 and is then supplied to an information extracting means 2. The information extracting means 2 extracts digital information presenting available metering rate and amount of money information from the signal supplied and then supplies the digital information to an information updating means 3.
The information updating means 3 outputs the detected information, for example, to a display unit (not shown) and also receives the update information corresponding to use. For example, in the case of the prepaid card used for the public telephone set, the information updating means 3 outputs a metering rate information read from the magnetic card and receives the update information such as the metering rate or reduction amount of metering rate after the metering rate used is subtracted by making a telephone call.
Next, the information updating means 3 generates the information updated depending on the update information received and supplies this updated information to a recording information generating means 4. The recording information generating means 4 generates a recording information including addition of header and an error correcting code and then outputs this recording information to a signal recording means 5. The signal recording means 5 newly records the information into the magnetic card 50.
As explained above, in the case of the prepaid card, for example, a user can receive various services such as telephone call from the public telephone set and shopping, as explained above, depending on the information recorded in the prepaid card by using this prepaid card.
In the case of a magnetic card such as a prepaid card explained previously, the information updating means 3 of the update apparatus shown in FIG. 1 is often controlled by a software. Therefore, information such as the available metering rate and amount of money information can easily be altered only by obtaining the update apparatus and then reprogramming the program installed in the information updating means 3.
Moreover, without relation to the update apparatus explained above, it is also possible that information of the magnetic card is rewritten unjustly to use it illegally by detecting information format recorded in the magnetic card.
Recently, various kinds of prepaid cards which may be used in a playground or an ordinary retailing shop in addition to the public telephone set and automatic ticket selling machine is also increasing. Moreover, various magnetic cards are used in various fields, for example, such as member card in which a personal information is recorded or a key card used in the hotel.
Therefore, it is a very important problem to effectively prevent altering of information recorded in the recording medium like a magnetic card for the purpose of wrong use.